Introduction:
The purpose of this experiment is to determine the hardness of a sample of water (#89).
Water hardness can be evaluated by an acid-base neutralization titration. (When an acid and a base are placed together, they react to neutralize the acid and base properties, producing a salt.) From the Bronsted-Lowry acid-base reaction theory, the H+ cation of the acid combines with the OH- anion of the base to form water. In this titration experiment, there are no definitive acidic or basic agents being evaluated. This requires the use of the Lewis acid-base theory.
Instead of defining acid-base reactions in terms of protons or other bonded substances, the Lewis definition defines a base (referred to as a Lewis base) to be a compound that can donate an electron pair, and an acid (a Lewis acid) to be a compound that can receive this electron pair. Similarly, in either type of acid-base neutralization experiment, an indicator is used to display when the solution is neutralized. The standardized Na2EDTA water solution is will be titrated against the unknown water sample (#89).
Upon neutralization, the unknown water sample’s metal cation electrons will transfer to the Na2EDTA solution and will subsequently remove the sodium from the EDTA. (Unknown #89)2+ + Na2EDTA → (Unknown #89)EDTA + 2Na+
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CHEMISTRY 122 CHAPTER 17 NOTES CHAPTER 17 EXERCISES (THESE ARE NOT TO BE TURNED IN, BUT QUIZ QUESTIONS WILL BE TAKEN FROM THESE EXERCISES SO IT IS TO YOUR BENEFIT TO DO THEM): 2, 3, 5, 6, 8, 10, 13, 15, 16, 18, 19, 21, 23, 25, 27, 28, 29, 31, 33, 37, 39, 41, 43, 44, 47, 48, 50, 53, 57, 60, 63, 64, 67, 70, 71, 73, 75, 78, 80, 87, 95, 102, 112 Chemistry of Acids and BasesSvante Arrhenius (1884) ...
Water hardness is expressed in in milligrams per liter.
Procedure:
The first thing to be done was to manufacture the 0.004 M Na2EDTA solution. This was done by adding 0.7319 g Na2EDTA to approximately 500 mL of DI water. I obtained a 50.0mL burret, a 10.00 mL and a 25.00 mL transfer pipet, and the unknown sample (#89) from the stockroom. The 50.0 mL burret was set in the burret stand. The Na2EDTA was in the burret and CaCO3 solution was in a 250 mL Erlenmeyer flask. The CaCO3 solution was comprised of 10.00 mL of 1.000g CaCO3/mL, approximately 30mL of DI water, 2.5 – 3.5 mL of buffer (ammonia/ammonium chloride), and 4 drops of Eriochrome Black T indicator. The Na2EDTA was being titrated against the CaCO3 while simultaneously being mixed by a magnetic stir bar in the 250 mL Erlenmeyer flask. The titration was run to completion when theCaCO3 solution turned from a violet to a blue color change.
This was done three times for the standardization of the Na2EDTA. The titration for the now standardized Na2EDTA solution against the unknown water sample #89 follows a similar procedure as the first titration except the contents of the 250 mL differ. The Unknown sample solution was comprised of 25.00 mL of unknown, approximately 20 mL of DI water, 2.5 – 3.5 mL of buffer (ammonia/ammonium chloride), and 4 drops of Eriochrome Black T indicator. The Na2EDTA was being titrated against the Unknown while simultaneously being mixed by a magnetic stir bar in the 250 mL Erlenmeyer flask. The titration was run to completion when the unknown solution turned from a violet to a blue color change. This was done three times to determine the hardness of water sample #89.
Experimental Data & Calculations:
1).
Na2EDTA & CaCO3 titration.
Na2EDTA solution:
0.7319 g & 500 mL DI Water
Trial #1:
CaCo3 Solution
Na2EDTA Solution
10 mL 1.000g CaCO3/L
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Every living thing is dependent on large complex molecules, known as macromolecules. The objective of this lab was to correctly identify which macromolecules the unknown solution was comprised of using various substances as experimental controls. There are four major types of biological macromolecules – carbohydrates, lipids, proteins, and nucleic acids – made up of elements such as ...
31 mL DI water
V0 = 0.60 mL
3.4 mL Buffer
Vf = 25.20 mL
4 drops Indicator
ΔV = 24.60 mL
Trial #2:
10 mL 1.000g CaCO3/L
30 mL DI water
V0 = 0.60 mL
3.3 mL Buffer
Vf = 23.92 mL
4 drops Indicator
ΔV = 23.22 mL
Trial #3:
10 mL 1.000g CaCO3/L
30 mL DI water
V0 = 0.50 mL
3.3 mL Buffer
Vf = 24.23 mL
4 drops Indicator
ΔV = 23.73 mL
2).
Na2EDTA & Unknown water sample #89 titration.
Trial #1:
Unknown Solution
Na2EDTA Solution
25 mL Unknown sample
20 mL DI water
V0 = 0.88 mL
3.0 mL Buffer
Vf = 13.80 mL
4 drops Indicator
ΔV = 12.92 mL
Trial #2:
25 mL Unknown sample
21 mL DI water
V0 = 18.60 mL
3.1 mL Buffer
Vf = 30.80 mL
4 drops Indicator
ΔV = 12.20 mL
Trial #3:
25 mL Unknown sample
20 mL DI water
V0 = 30.80 mL
2.9 mL Buffer
Vf = 43.20 mL
4 drops Indicator
ΔV = 12.20 mL
Na2EDTA molarity equation:
Na2EDTA ΔV
Na2EDTA molarity
Trail #1 = 24.6 mL
0.0040 M
Trail #2 = 23.22 mL
0.0042 M
Trail #3 = 23.73 mL
0.0042 M
Na2EDTA mean molarity:
Absolute Deviation:
Trail #1 = 0.0001 M Na2EDTA
Trail #2 = 0.0001 M Na2EDTA
Trail #3 = 0.0001 M Na2EDTA
Estimated precision:
Estimated precision = 0.1 ppt.
Calculating Water Hardness (parts per million):
M mol Na2EDTA = [Na2EDTA]mean = 0.0041 M
Trail #1 ΔV = 12.92 mL = 216.4 ppm
Trail #2 ΔV = 12.20 mL= 204.3 ppm
Trail #3 ΔV = 12.20 mL= 207.7 ppm
Parts Per Million Mean Calculation :
Discussion:
There are two tangibles that I feel may have affected the results of my calculations. The first was being able to use the transfer pipet correctly. I recall two trials where there was a combination of having bubbles in the pipet and adding an excess of the limiting reagent. The other struggle for me in this lab was being able to effectively determine the reaction’s completion by color change. An unnecessary excess of NaEDTA may have been added to determine the reactions completion. These two pitfalls in my method can explain for the error in my work.
The Term Paper on Hardness Of Water Edta Ppm Tap
Water is the most important molecule that exists on the Earth. Without water living beings would not be able to live. Water is used for an immeasurable number of things. There are many properties of water, which makes this molecule so unique. One which people overlook is hardness. Hardness is defined in the Chemistry: The Central Science by Prentice Hall's as being "water that contains a ...
For practical purpose, water hardness values less than 60 ppm is “soft”, while water with more than 200 ppm is considered “hard.” The analysis of my unknown sample came out to be 209 ppm, a “hard” water sample. To present some validity to my result, I can briefly compare the water hardness’s of my unknown water sample to the 1.000 g CaCO3. The CaCO3 solution has a hardness of 1000 ppm and my calculated unknown has a hardness of 209 ppm. Since the CaCO3 has a higher hardness value, this is why it took more Na2EDTA to neutralize it in the first sets of titrations. This assures me that my calculated result should be less than 1000 pmm.
